Threesome??

Okay so a little background. My husband has always hint that he wants a "pet" which is like a 3rd party in our relationship. I've always been against it scared he'll leave me for the other woman. Well going back 2 weeks I had some friends over drinking and we were having a good time. Then everything went Blank. I remember pieces but not much. My husband said that I ended up kissing than taking my friend to our room and start making out. We ended up having a threesome that I DONT Remember. ever since my husband has been trying to get her to come over more often and talks about her a lot.. I know I made a mistake while drunk but how can I tell my husband to stop talking about it.